An increasing interest in the evaluation human emotions may be seen in the behavioral, biological, and social sciences. Many phenomena, ranging from individual cognitive processing to social and collective behavior, may not be well understood without taking human emotions into account. Recently, there has been an interest in affective computing, which is the study and development of computing systems or devices that can recognize, interpret, process, and simulate human affects. In particular, the emotion of the user may be used as an input for subsequent operations by computing devices or systems.